Integrity Evaluation of Composite Cylindrical Structures

The application of composite material in structures can not only lower the component weight but also improve the system performance through its tailorable thermal and mechanical properties. However, because of the harsh environmental conditions that such structures may encounter during operation, the successful applications of such structures cannot be realized without appropriate techniques for their structural integrity evaluation. In this study, composite cylindrical structures consisting of composite and steel layers are being evaluated with X-ray diffraction technique and various ultrasound techniques. First, X-ray diffraction technique was applied for the quantitative determination of the residual stress in the steel layer. The influence of composite layer on the stress distribution was analyzed and how such residual stress study will improve the performance of the structure was discussed. Then various ultrasound techniques were applied for the detection of various defects, such as the defects at the surface and subsurface of inner steel layer, the different types of defects in the outer composite layer, and the defect, which is the most critical one, at the interface of steel/composite layer. During ultrasound evaluation, the composite material may not only increase the ultrasound attenuation but also change ultrasound traveling direction, and this can make the inspection more challenging. Theoretical calculations were carried out for the optimization of experimental parameters such as ultrasound frequency, incident angle, and focused ultrasound field calculation and so on. The limitations of ultrasound technique and the potential of other non-destructive techniques were also discussed according to experimental results.